1. Field of the Invention
The present invention relates to a database system capable of dealing with dynamic changes in an event.
2. Description of the Background Art
In recent years, along with the developments of computer systems and computer networks, databases that store and manage a great amount of computerized data has been widely used. In these databases, a relational database (RDB), in which data describing events is represented by two-dimensional tables and the relation between the tables is defined, has been mainly used. In the RDB, in most cases, the data structure is standardized in order to provide efficient database operations.
However, in the case of the RDB having the standardized data structure, it becomes difficult to locally operate data, and the resulting disadvantage is that it is not possible to flexibly deal with changes in an event. For this reason, various techniques have been developed to flexibly deal with changes in an event.
With respect to the techniques for flexibly dealing with changes in an event, mainly two techniques have been proposed: a technique of flexibly changing the data structure in response to changes in an event; and a technique of flexibly changing an accessing method to the database in response to changes in an event.
With respect to the technique of flexibly changing the data structure in response to changes in an event, a technique of an object oriented database (OODB) in which data and an algorithm are integrally prepared so that local data operations can be carried out has been proposed (Japanese Patent Application Laid-Open No. 2001-331315). Moreover, another technique which uses an architectural database having an architectural data structure has been proposed (Japanese Patent Application Laid-Open No. 11-296544 (1999)). The technique disclosed in Japanese Patent Application Laid-Open No. 11-296544 (1999) features in that the history of changes in a data structure is stored, and that, even when there is a change in the data structure, the structure prior to the change is accessible.
Moreover, with respect to the technique of flexibly changing an accessing method to the database in response to changes in an event, a technique which utilizes a user profile in which the history of a user's database operations is written for an assisting purpose so as to improve the database accessing efficiency has been proposed (Japanese Patent Application Laid-Open Nos. 11-53394 (1999) and 2002-230021).
In accordance with the techniques of Japanese Patent Application Laid-Open Nos. 2001-331315 and 11-296544 (1999), although it is possible to flexibly deal with changes in a singly-occurring event, it is not possible to deal with dynamic changes in an event that is continuously varied with time.
Moreover, in accordance with the techniques of Japanese Patent Application Laid-Open Nos. 11-53394 (1999) and 2002-230021, it is also possible to deal with changes in an event. However, these techniques are based on the assumption that the data of a database to be accessed has a specific data structure. Further, these techniques do not function sufficiently unless this data structure properly reflects the corresponding event. For this reason, even in the case when these techniques become effective immediately after the start of the application of the database, the database accessing operation becomes inefficient when the data structure fails to maintain an optimal state due to changes in an event. In other words, these techniques fail to effectively deal with dynamic changes in an event that is continuously varied with time.